By setting adding the uses-feature tag for touchscreens and android:required="false" to it, it tells Google Play and the Android runtime that this app doesn't require touchscreens, making Google Play and the OS treat it as if it'll work on non-touch devices.

Also it's possible to add android:required="false" to the Bluetooth tag as it's not needed for adding contacts, I'm just not sure how the Briar app would react on an Android device that doesn't support Bluetooth so I didn't take that leap.